Wireless communication systems, such as the 3rd Generation (3G) of mobile telephone standards and technology, are well known. An example of such 3G standards and technology is the Universal Mobile Telecommunications System (UMTS™), developed by the 3rd Generation Partnership Project (3GPP™) (www.3gpp.org).
The 3rd and 4th generations of wireless communications, and particular systems such as LTE, have generally been developed to support macro-cell mobile phone communications. Here the ‘phone’ may be a smart phone, or another mobile or portable communication unit that is linked wirelessly to a network through which calls are connected. Henceforth all these devices will be referred to as mobile communication units. Calls may be data, video, or voice calls, or a combination of these. Such macro cells utilise high power base stations to communicate with wireless communication units within a relatively large geographical coverage area. The coverage area may be several square kilometers, or larger if it is not in a built-up area.
Typically, mobile communication units, or User Equipment as they are often referred to in 3G, communicate with a Core Network of the 3G wireless communication system. This communication is via a Radio Network Subsystem. A wireless communication system typically comprises a plurality of Radio Network Subsystems. Each Radio Network Subsystem comprises one or more cells, to which mobile communication units may attach, and thereby connect to the network. A base station may serve a cell. Each base station may have multiple antennas, each of which serves one sector of the cell.
Operators of wireless communication systems need to know what is happening in the system, with as much precision as possible. A particular issue is the need to solve ‘faults’. Faults may take a wide variety of forms, but can be summarised as events when the network and/or one or more mobile communication units do not perform as expected.
Modern wireless communication systems allow a high degree of autonomy to individual mobile communication units and to base stations. As a consequence, decisions about setting up and ‘tearing down’ call links throughout the network are not all made centrally. An additional complication arises from the volume of information generated within the wireless communication system. In one day, a wireless communication system may generate 100 gigabytes of data about calls that have been made in the network.
This volume of data has proved a major obstacle to fault location in existing wireless communication systems. Network operators have not been able to install sufficiently large memories to store this information, with acceptable access times.
Some conventional systems do store all data generated in a network, using expensive storage technology. These approaches then involve attempting to access one or more individual records, as and when an enquiry about a particular mobile communication unit or call is received.
Three other conventional approaches to finding out what has happened in the network do not rely on storing all data from the mobile radio communications network. These approaches are referred to under separate sub-headings below as ‘Approach 1’, ‘Approach 2’ and ‘Approach 3’.
Approach 1
A user of a mobile communication unit may notify the network operator of a fault. In this case, staff at the network operator's operations centre will typically arrange for data to be captured for a limited part of the network, for a limited time period. For example, the wireless communication network may be ‘probed’, to collect data. The probe may be installed in the wireless communication network for a period of up to 24 hours, typically, and monitor one sector of the network. Even though data is only gathered comprehensively for a very limited part of the wireless communication network, for only a few hours, the volume of data collected is still very great.
The data is typically analysed as a batch, after the end of the monitoring period. Expert staff may be required to interpret the results. If particular additional calculations often need to be performed, such as ‘geolocating’ a mobile communication device, then this may add to the total delay.
There are many disadvantages of this approach, including that:                (i) The results are often first available more than a day after a fault has been reported.        (ii) The fault may only be detected if it re-occurs during the period for which the probe is gathering data.        (iii) The fault may only be detected if the probe has been installed in the correct sector of the network.        (iv) There is significant scope for operator error.        
Approach 2
Some network operators try to derive high level statistics for the operation of their network. A typical approach is to take a small sample of the calls occurring, across multiple sectors or the whole network. If the sample is large enough, then a representative sample of calls for most or all sectors will be available. These can then be used to develop indicators of what is happening in the network.
For example, it may be possible to say what percentage of the calls of the sample for a given sector were ‘dropped’. ‘Dropped’ calls are calls that did not end with termination by either participant in the call, but by the network or one mobile communication unit being no longer able to maintain the communication link. So a network operator may know, in this example, that 2% of the sample of calls in a particular sector were dropped, in a given time period. From this, if the sample was large enough, it may be reasonable to infer that 2% of all the calls that actually took place, were dropped. This may be of use in indicating that one sector has a higher rate of dropped calls than the mean rate for other sectors. However, such information is only an indication that there may be some kind of problem in a sector. This does not help diagnose why a particular user is reporting faults.
The statistics that can be produced often do not provide fine enough detail for a network operator to derive reliable fault diagnosis information. For example, if an antenna covering a particular sector is not at the optimal angle, this may not be revealed. If a particular class of mobile communications unit, such as a new design of smartphone, is not operating reliably within the sector, then the operator may not have the evidence to demonstrate this.
Approach 3
Network operators conduct ‘drive tests’ through a network. A vehicle is driven through the mobile communications network, and parameters such as signal strength are measured at the various locations that the vehicle can access. This approach may be undertaken routinely, or may be instigated after approaches 1 or 2 indicate that there may be a problem in a sector.
A growing proportion of calls are now being made within buildings. However, vehicles are restricted to roads and parking areas, so drive tests cannot provide information about why a user within a building experiences a fault. In addition, drive tests are likely to occur even later than the monitoring described under approach 1, so may involve even more days of delay, before a fault can be diagnosed.